linux-kernel - Re: [PATCH 08 of 11] anon-vma-rwsem

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Message-ID: <alpine.LFD.1.10.0805071349200.3024@woody.linux-foundation.org>
Date:	Wed, 7 May 2008 13:56:23 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrea Arcangeli <andrea@...ranet.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <clameter@....com>,
	Jack Steiner <steiner@....com>, Robin Holt <holt@....com>,
	Nick Piggin <npiggin@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	kvm-devel@...ts.sourceforge.net,
	Kanoj Sarcar <kanojsarcar@...oo.com>,
	Roland Dreier <rdreier@...co.com>,
	Steve Wise <swise@...ngridcomputing.com>,
	linux-kernel@...r.kernel.org, Avi Kivity <avi@...ranet.com>,
	linux-mm@...ck.org, general@...ts.openfabrics.org,
	Hugh Dickins <hugh@...itas.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Anthony Liguori <aliguori@...ibm.com>,
	Chris Wright <chrisw@...hat.com>,
	Marcelo Tosatti <marcelo@...ck.org>,
	Eric Dumazet <dada1@...mosbay.com>,
	"Paul E. McKenney" <paulmck@...ibm.com>
Subject: Re: [PATCH 08 of 11] anon-vma-rwsem



On Wed, 7 May 2008, Andrea Arcangeli wrote:
> 
> Convert the anon_vma spinlock to a rw semaphore. This allows concurrent
> traversal of reverse maps for try_to_unmap() and page_mkclean(). It also
> allows the calling of sleeping functions from reverse map traversal as
> needed for the notifier callbacks. It includes possible concurrency.

This also looks very debatable indeed. The only performance numbers quoted 
are:

>   This results in f.e. the Aim9 brk performance test to got down by 10-15%.

which just seems like a total disaster.

The whole series looks bad, in fact. Lack of authorship, bad single-line 
description, and the code itself sucks so badly that it's not even funny.

NAK NAK NAK. All of it. It stinks.

		Linus
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